The present invention relates to rotation sensors, such as gyroscopes, and particularly to a fiber optic rotation sensor which has an extended dynamic range.
Fiber optic rotation sensors typcially comprise a loop of fiber optic material to which light waves are coupled for propagation around the loop in opposite directions. Rotation of the loop creates a relative phase difference between counter-propagating waves, in accordance with the well known "Sagnac effect", with the amount of phase difference corresponding to the velocity of rotation. The counter-propagating waves, when recombined, interfere constructively or destructively to produce an optical output signal which varies in intensity in accordance with the rotation rate of the loop. Rotation sensing is commonly accomplished by detection of this optical output signal.
Various techniques have been devised to increase the sensitivity of fiber optic rotation sensors to small rotation velocities. However, these techniques do not work for very large rotation velocities because the output functions tend to repeat themselves at various velocities of rotation such that it cannot be determined from the output signal which of the possible rotation velocities which have the same output signal waveform is responsible for the particular output signal waveform observed.
The present invention provides a way to extend the dynamic range of the fiber optic gyroscope to larger rotational velocities.